The underground location of lines and conduit for the many utilities in service today means that replacement of existing lines with new conduit lines is more complicated and necessitated due to age and deterioration, accidental breaks or population and usage growth making existing lines obsolete. Often the lines were installed with open trenches many years ago and subsequently new developments, such as roads, housing or landscaping have gone in over the surface, thus making re-excavation impossible or unacceptable. Also excavation methods are expensive in man power, equipment and risk of injury or damage.
There are numerous methods in use and available to replace old or outdated lines with new line material and without extensive excavation, but each has a variety of drawbacks or limitations. The commonly used method to replace pipe without excavation of which this invention is an improvement is called pipe bursting. Streaffield, U.S. Pat. No. 4,738,565 is one such method. It makes use of a conical shaped mole that is forced through an existing pipe and, in turn, pulls the new piping into the space. The bursting occurs when the mole is forced into the pipe. The mole is shaped such that it is smaller than the inside diameter of the old pipe at one end of the mole and larger than the inside diameter of the pipe at the other end of the mole and thus causes the original pipe to be fractured or, by other methods, cut. The object is to destroy and displace or remove the original pipe structure to then allow the new replacement pipe's structure to take the place of the original. Thus the new pipe replaces the old pipe without excavating along the entire length of the pipe being replaced.
The methods, such as the above, however, generally require that two excavations be made--one at the start of the pipe bursting and the second at the end. This then accomplishes the replacement in that section. If more than one section is to be replaced, then successive points of excavation are made to accommodate the equipment and tools used to force the mole to do its job. For the mole tool to be started in the correct manner at the start of the hole a large excavation is necessary and another large excavation is needed to allow the mole tool to be removed at the end joint. Most of the current methods make use of equipment and tools that require the end point to be excavated even if there is access through a manhole vault at the location because the removal of the tool at the end requires a larger opening than the manhole vault. This causes problems as the manholes themselves are expensive structures to replace. Usually a manhole vault is in the system and often is located in a roadway. The previous methods require excavation of the manhole or vault which means that the excavation will impede traffic while the excavation is made, used and finally replaced and repaired. The necessity to excavate in streets is often regulated by local government to prevent an unacceptable number or timing of street cuts. Thus construction projects may have to be delayed for city permits.